Wow that is tiny!
Fart eggs are the tiniest and in our case was the prelude to a 5-1/2 yr old Silkie hen w/ developing reproductive issue -- eventually a bleeding ovarian tumor. She also layed an egg w/ rubbery texture, & also no shell egg. Sadly she was put down at 6-1/2 yrs old at the vet.
Fart egg
Misshapen rubbery